Nimitz was the leading US Navy authority on submarines. Qualified in submarines during his early years, he later oversaw the conversion of these vessels' propulsion from gasoline to diesel, and then later was key in acquiring approval to build the world's first nuclear-powered submarine, USS Nautilus, whose propulsion system later completely superseded diesel-powered submarines in the US. He also, beginning in 1917, was the Navy's leading developer of underway replenishment techniques, the tool which during the Pacific war would allow the US fleet to operate away from port almost indefinitely. The chief of the Navy's Bureau of Navigation in 1939, Nimitz served as Chief of Naval Operations (CNO) from 1945 until 1947. He was the United States' last surviving officer who served in the rank of fleet admiral.

Nimitz returned to the United States on board USS Ranger when that vessel was converted to a school ship, and in January 1909, began instruction in the First Submarine Flotilla. In May of that year, he was given command of the flotilla, with additional duty in command of USS Plunger, later renamed A-1. He commanded USS Snapper (later renamed C-5) when that submarine was commissioned on February 2, 1910, and on November 18, 1910 assumed command of USS Narwhal (later renamed D-1).[8]

In the latter command, he had additional duty from October 10, 1911 as Commander 3rd Submarine Division Atlantic Torpedo Fleet. In November 1911, he was ordered to the Boston Navy Yard, to assist in fitting out USS Skipjack and assumed command of that submarine, which had been renamed E-1, at her commissioning on February 14, 1912. On the monitorTonopah on March 20, 1912, he rescued Fireman Second Class W. J. Walsh from drowning, receiving a Silver Lifesaving Medal for his action.[8]

After the United States declared war on Germany in April 1917, Nimitz was Chief Engineer of Maumee while the vessel served as a refueling ship for the first squadron of U.S. Navy destroyers to cross the Atlantic, to take part in the war. Under his supervision, Maumee conducted the first-ever underway refuelings. On August 10, 1917, Nimitz became aide to Rear Admiral Samuel S. Robison, Commander, Submarine Force, U.S. Atlantic Fleet (COMSUBLANT).

On February 6, 1918, Nimitz was appointed chief of staff and was awarded a Letter of Commendation for meritorious service as COMSUBLANT's chief of staff. On September 16, he reported to the office of the Chief of Naval Operations, and on October 25 was given additional duty as Senior Member, Board of Submarine Design.

In April 1935, Nimitz returned home for three years as assistant chief of the Bureau of Navigation, before becoming commander, Cruiser Division 2, Battle Force. In September 1938. he took command of Battleship Division 1, Battle Force. On June 15, 1939, he was appointed chief of the Bureau of Navigation. During this time, Nimitz conducted experiments in the underway refueling of large ships which would prove a key element in the Navy's success in the war to come.

Ten days after the attack on Pearl Harbor on December 7, 1941, he was promoted by Roosevelt to commander-in-chief, United States Pacific Fleet (CINCPACFLT), with the rank of admiral, effective December 31. He immediately departed Washington for Hawaii and took command in a ceremony on the top deck of the submarine Grayling. The change of command ceremony would normally have taken place aboard a battleship, but every battleship in Pearl Harbor had been either sunk or damaged during the attack. Assuming command at the most critical period of the war in the Pacific, Admiral Nimitz successfully organized his forces to halt the Japanese advance despite the losses from the attack on Pearl Harbor and the shortage of ships, planes, and supplies.

As rapidly as ships, men, and materiel became available, Nimitz shifted to the offensive and fought the Japanese navy in the Battle of the Coral Sea – a tactical victory for the Japanese in terms of ships sunk, but a strategic victory for the Allies for several reasons – in the pivotal Battle of Midway, and in the Solomon Islands campaign. The severe losses in carriers at Midway prevented the Japanese from re-attempting to invade Port Moresby from the ocean. The Allies took advantage of Japan's resulting strategic vulnerability in the South Pacific and launched the Guadalcanal Campaign that, along with the New Guinea Campaign, eventually broke Japanese defenses in the South Pacific.

By Act of Congress, passed on December 14, 1944, the grade of Fleet Admiral — the highest grade in the Navy — was established and the next day PresidentFranklin Roosevelt appointed Nimitz to that rank. Nimitz took the oath of that office on December 19, 1944.

In January 1945, Nimitz moved the headquarters of the Pacific Fleet forward from Pearl Harbor to Guam for the remainder of the war. Mrs. Nimitz remained in the continental United States for the duration of the war, and did not join her husband in Hawaii or Guam.

On September 2, 1945, Nimitz signed for the United States when Japan formally surrendered on board USS Missouri in Tokyo Bay. On October 5, 1945, which had been officially designated as "Nimitz Day" in Washington, D.C., Admiral Nimitz was personally presented a Gold Star for the third award of the Distinguished Service Medal by Harry S. Truman "for exceptionally meritorious service as Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, from June 1944 to August 1945."

On November 26, 1945, his nomination as Chief of Naval Operations was confirmed by the U.S. Senate, and on December 15, 1945, he relieved Fleet Admiral Ernest J. King. He had assured the President that he was willing to serve as the CNO for one two-year term, but no longer. He tackled the difficult task of reducing the most powerful navy in the world to a fraction of its war-time strength, while establishing and overseeing active and reserve fleets with the strength and readiness required to support national policy.

Nimitz endorsed an entirely new course for the U.S. Navy's future by way of supporting then-Captain Hyman G. Rickover's chain-of-command-circumventing proposal in 1947 to build USS Nautilus, the world's first nuclear-powered vessel.[11] As is noted at a display at the Nimitz Museum in Fredericksburg, Texas: "Nimitz's greatest legacy as CNO is arguably his support of Admiral Hyman Rickover's effort to convert the submarine fleet from diesel to nuclear propulsion."

From 1949 to 1953, Nimitz served as UN-appointed Plebiscite Administrator for Jammu and Kashmir.[12] His proposed role as administrator was accepted by Pakistan but rejected by India.[13][14]

On December 15, 1947, Nimitz retired from office as Chief of Naval Operations and received a third Gold Star in lieu of a fourth Navy Distinguished Service Medal. However, since the rank of fleet admiral is a lifetime appointment, he remained on active duty for the rest of his life, with full pay and benefits. He and his wife, Catherine, moved to Berkeley, California. After he suffered a serious fall in 1964, he and Catherine moved to US Naval quarters on Yerba Buena Island in the San Francisco Bay.

In San Francisco, Nimitz served in the mostly ceremonial post as a special assistant to the Secretary of the Navy in the Western Sea Frontier. He worked to help restore goodwill with Japan after World War II by helping to raise funds for the restoration of the Japanese Imperial Navy battleship Mikasa, Admiral Heihachiro Togo's flagship at the Battle of Tsushima in 1905.

He was also appointed as the United Nations Plebiscite Administrator for Kashmir, but owing to disagreements between India and Pakistan over demilitarization, that mission did not take place. [15]

Nimitz became a member of the Bohemian Club of San Francisco. In 1948, he sponsored a Bohemian dinner in honor of U.S. Army General Mark Clark, known for his campaigns in North Africa and Italy.[16]

Nimitz served as a regent of the University of California during 1948–1956, where he had formerly been a faculty member as a professor of naval science for the NROTC program. Nimitz was honored on October 17, 1964, by the University of California on Nimitz Day.

Catherine Vance graduated from the University of California, Berkeley, in 1934,[24] became a music librarian with the Washington D.C. Public Library,[25] and married U.S. Navy Commander James Thomas Lay (1909–2001[26]), from St. Clair, Missouri, in Chester and Catherine's suite at the Fairfax Hotel in Washington, D.C., on March 9, 1945.[27] She had met Lay in the summer of 1934 while visiting her parents in Southeast Asia.[24]

Chester Nimitz, Jr., graduated from the U.S. Naval Academy in 1936 and served as a submariner in the Navy until his retirement in 1957, reaching the (post retirement) rank of rear admiral; he served as chairman of PerkinElmer from 1969–1980.

Sister Mary Aquinas (Nimitz) became a sister in the Order of Preachers (Dominicans), working at the Dominican University of California. She taught biology for 16 years, and was academic dean for 11 years, acting president for one year, and vice president for institutional research for 13 years before becoming the university's emergency preparedness coordinator. She held this job until her death, due to cancer, on February 27, 2006.

Commodore – no longer a rank in the United States Navy, was previously reserved for wartime use and was not in use at the time of Nimitz's promotion to flag rank. Currently, a captain who is promoted to pay grade O-7 becomes a rear admiral (lower half) and uses the abbreviated rank designation RDML as opposed to RADM, which designates a rear admiral (upper half), O-8. During Admiral Nimitz's service, the only rank existing among these was rear admiral, without distinction between upper and lower half.

At the time of Nimitz's promotion to rear admiral, the United States Navy did not maintain a one-star rank (Commodore). Nimitz was thus promoted directly from a captain to rear admiral. By Congressional appointment, he skipped the rank of vice admiral and became an admiral in December 1941.

Nimitz also never held the rank of lieutenant junior grade, as he was appointed a full lieutenant after three years of service as an ensign. (For administrative reasons, Nimitz's naval record states that he was promoted to the rank of lieutenant junior grade and lieutenant on the same day.)[citation needed]

Borneman, Walter R. (2012). The Admirals: Nimitz, Halsey, Leahy and King – The Five-Star Admirals Who Won the War at Sea(Hardback)|format= requires |url= (help). New York: Little, Brown and Company. ISBN978-0-316-09784-0.

Texas Navy hosted by The Portal to Texas History. A survey of the Texas Navy during the Texas Revolution and the Republic Era. Includes maps, sketches, a list of ships of the Texas Navy, and a chronology. Also includes photographs of 20th century U.S. Navy ships named after Texans or Texas locations. See photos of Chester Nimitz and the Nimitz hotel.